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488.cpp
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488.cpp
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class Solution {
public:
string clear(string board) {
int n = board.size();
int index = 0;
while (index < n) {
char c = board[index];
int start = index;
while (index + 1 < n && board[index + 1] == c) index++;
if (index - start + 1 >= 3) {
string next = board.substr(0, start) + board.substr(index + 1);
return clear(next);
}
index++;
}
return board;
}
int dfs(string board, vector<int>& counts, unordered_map<string, int>& memo) {
if (board.size() == 0) return 0;
string key = board + "#" + encodeFreq(counts);
if (memo.find(key) != memo.end()) return memo[key];
int n = board.size();
int res = INT_MAX;
for (int i = 0; i < n; ++i) {
for (int j = 0; j < 5; ++j) {
bool toTry = false;
if (mapping(board[i]) == j) toTry = true;
if (i > 0 && board[i] == board[i - 1] && mapping(board[i]) != j) toTry = true;
if (counts[j] > 0 && toTry) {
board.insert(board.begin() + i, reverseMapping(j));
string next = clear(board);
counts[j]--;
int steps = dfs(next, counts, memo);
if (steps != INT_MAX) res = min(res, steps + 1);
counts[j]++;
board.erase(board.begin() + i);
}
}
}
memo[key] = res;
return res;
}
int mapping(char c) {
switch (c) {
case 'R':
return 0;
case 'Y':
return 1;
case 'B':
return 2;
case 'G':
return 3;
default:
return 4;
}
return 4;
}
char reverseMapping(int i) {
switch (i) {
case 0:
return 'R';
case 1:
return 'Y';
case 2:
return 'B';
case 3:
return 'G';
default:
return 'W';
}
return 'W';
}
string encodeFreq(vector<int>& counts) {
string res;
for (int i = 0; i < 5; ++i) {
res += to_string(counts[i]);
res += "#";
}
return res;
}
int findMinStep(string board, string hand) {
vector<int> counts(5, 0);
for (auto c : hand) counts[mapping(c)]++;
unordered_map<string, int> memo;
int res = dfs(board, counts, memo);
if (res == INT_MAX) return -1;
return res;
}
};